Neutrodyning for short waves



May 31, 1949. G. AVHIERY ET AL 2,471,401

NEUTRODYNING FOR SHORT WAVES Filed March 20, 1947 292 2a FIG.1

27 l0 l4 l3 We 2| 3o I7 u I2 22 2 24 PRIMARY CIRCUIT M OSCILLATIONS (NEUTRODYNE cmcun FIG. 3

SECONDARY CIRCUIT 05 CILLATIO NS INVENTOR rE RGEs AH/E'R Y EM -E TOURATON ATTORNEY Patented May 31, 1949 NEUTRODYNING FOR SHORT WAVES Georges Ahier and Emile Touraton, Paris, France, assignors to International Standard Electric Corp., New York, N. Y., a corporation of Delaware Application March 20, 1947, Serial No. 735,908 In France June 18, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires June 18, 19.65

7 Claims.

This invention relates to a spark gap type short wave generator, and more particularly to a radio transmitter utilizing a series resonant circuit in the primary coupled to a parallel resonant circuit in the secondary to substantially prevent a secondary reaction on the spark gap after the initial primary discharge across the spark gap has been dissipated.

Due to a neutrodyning action created by a capacitive coupling between the primary and secondary circuits of the generator, the re -ignition of a spark from the secondary circuit back to the primary circuit is retarded.

An important object of the invention is to prevent, in a spark transmitter, the reaction of the secondary oscillatory circuit on the primary oscillatory circuit containing the spark gap and obtain a neutrodyne action.

Another object of the invention is a provision for installing coupling capacitors in such a way as to obtain an electrostatic coupling that is reversed with respect to the electromagnetic coupling of the inductors in the resonant circuits at wavelengths shorter than about ten meters.

Another object is to provide a radio transmitter circuit employing a primary series resonant cir cuit coupled to a secondary parallel resonant circuit to restrict or substantially prevent secondary reaction on the spark gap to obtain an output having a substantially linear wave shape at wavelengths shorter than about ten meters.

A further object of the invention is to provide a spark gap generator of the class set forth, which is of an extremely simplified but durable and eflicient construction and arrangement of parts, and which will be comparatively inexpensive to manufacture.

Other and further objects may be and may become apparent to those skilled in the art from a perusal of this invention without departing from the spirit of the subjoined claims.

For a better understanding of the invention, reference may be had to the accompanying drawings.

In the drawings:

Fig. 1 is a schematic diagram of the circuit of a conventional spark transmitter, for comparison with the circuit of the present invention.

Fig. 2 illustrates schematically the configuration of the oscillations received at the terminals 2 of the primary and secondary circuits when spark re-ignition occurs in a circuit as shown in Fig. 1.

Fig. 3 illustrates schematically the configuration of the oscillations received at the terminals of the primary and secondary circuits without spark reignition as employed in the invention as shown in the circuit of Fig. 4.

Fig. 4 is a schematic diagram of a neutrodyne circuit of a spark transmitter embodying the invention.

Referring more particularly to the drawing, there is shown in Fig. 1 two terminals i0 and H, the terminal II is connected to the ground by a lead [2 and the terminal I0 is connected to a resistor 13 by a lead 14. The other end of the resistor i3 is connected to one side of a spark gap I5 by a lead 16 and to a plate of a capacitor 11 by a lead l8. One side of a primary coil 19 of a transformer 20 is connected to the spark gap 15 by a lead 2|. The'other side of the primary coil I 9 is connected to a plate of a capacitor l'l' by a lead 22 and this lead is connected to the ground. One side of a secondary coil 23 of the transformer 20 is connected to one plate of a capacitor 24 by a lead 25 and the other side of the secondary coil 23 is connected to the other plate of capacitor 24 by a lead 26 and this lead is connected to the ground. One side of an antenna coupling coil 21 is connected to the ground by a lead 30.

In Fig. 4 there is shown a voltage source 31 connected to a resistor 32 by a lead 33 and also connected to a second resistor 34 by a lead 35. The resistor 32 is then connected to an inductor 36 by a lead 31. The resistor 34 is connected to a second inductor 38 by a lead 39. The plates of a capacitor 40 are connected to the leads 3'! and 39 by leads 4| and 42 respectively. The inductor 36 is connected to one plate of a second capacitor 43 by a lead 44 and the second inductor 38 is connected to a third capacitor 45 by a lead 46. A spark gap 41 is connected with the leads 44 and 4G by leads 48 and 49 respectively. The second plate of the second capacitor 43 is connected to one side of a third inductor 50 and to one plate of a fourth capacitor 5| by a lead 52 and the second plate of the capacitor 45 is connected to the other side of the inductor 50 and the second plate of the capacitor 5| by a lead 53. The midpoint or the inductor 50 is connected to the ground. One side of an antenna coil 54 is con- 3 nected to the antenna 55 by a lead 56 and the other side of the antenna coil 54 is connected to the ground by a lead 51.

In operation, employing the circuit shown in Fig. 1, there is a voltage applied at the terminals and H, which, across the resistor I3, excites an oscillatory circuit comprising the capacitor H, the spark gap l and the induction coil l9. This primary circuit is coupled to a secondary circuit comprising essentially the induction coil 23 and the capacitor 24, itself loosely coupled to a radiating system which is comprised of the antenna coil 21 and the antenna 28. Upon application of the voltage to the primary circuit the capacitor I1 is charged and a spark produced across the terminals of the spark gap is which in tum creates oscillations of a frequency determined by the value of the capacitor l1 and the inductor l9. The secondary circuit is tuned to resonate at this frequency and there is induced in this circuit os- 1 cillations of like frequency and amplitude of those created in the primary circuit.

Figure 2 illustrates schematically the phenomena, as observed in short waves, that then occur at A in the primary circuit and at B in the secondary circuit. A beat system sets up between the primary and secondary .circuits. At the moment C when the energy becomes zero in the primary circuit, it is on the contrary maximum in "the secondary circuit, as shown at C. Due to the coupling that exists between the resonant circuits, the secondary circuit then reacts on the primary circuit and re-ignites the spark which had become extinguished shortly before reaching point C, which corresponds to the time when the capacitor ll has completely released its charge and the cycle begins anew. The phenomenon accordingly continues until renewed .at point D. Under these conditions, the system does not operate as single wave.

The Wien method makes it possible, in the :known manner, to avoid this re-ignition and to obtain oscillations like those whose curves are shown in Fig 3 and are essentially linear in wave shape. This method, however, is only applicable to spark gap generators operating on sufficiently long waves. The difiiculties of de-energization occur again when dealing with waves whose length is less than about meters.

The present invention aims precisely at pro 'viding a process that will prevent the re-ignition as illustrated in Fig. .2 when use is made of a spark station operating on a wavelength of less than aboutlO meters.

Fig. 4 illustrates a spark station which is fed acrossthe resistors 32 and 34 by a voltage source 3| whose mid-point is grounded. The ends of the induction coils 36 and 38 that belong to the primary circuit are connected to the ends of the induction coil 50 of the secondary circuit by the two capacitors 43 and 45, An electromagnetic coupling is set up respectively between the induction coils 36 and 38 and the halves of the induction coil 5i]. The mid-point of the coil5fl is placed at ground potential. The condensers 43 and 45, by means of which the capacitive coupling cat the vtwo circuits is efiected, are arranged with respect to the windings of the induction coils so that the electrostatic coupling of the circuits is in .reverse direction to their electromagnetic coupling. Since the voltage induced by magnetic coupling upon de-energization of .the spark gap is compensated by the voltage proceeding from the capacitive coupling, re-ignition is made impossible.

Therefore, with wavelengths shorter than about 7-5 10 meters, there is obtained the configuration of the representative values as those shown in Fig. 3.

The values shown in Fig. 2 are representative of the action in the circuit of Fig. 1. In the primary circuit, when the voltage is at zero at point C the voltage is at a maximum in the secondary circuit as shown at point C. Due to the collapse of the secondary field a back electromotive force is exerted on the primary circuit which causes a second or induced spark across the gap 15, thereby creating a non-linear sinusoidal wave in the antenna circuit.

The values shown in Fig. 3 are representative of the action in a neutrodyne spark gap circuit, as :showninFig. 4, whereby the voltage induced into thesecondary circuit produces a linear sinusoidal wave in the antenna circuit but back-electromotive force is cancelled due to the interaction of the electrostatic and electromagnetic fields neutralizing each other.

From the foregoing it will be seen that a series resonant primary circuit consisting of the inductances 36, 38, and the capacitor 40, are connccted to the spark gap 41. A parallel resonant secondary circuit consisting of the inductance 50 .and the capacitor 5| has the input connected electrostatically by means of the condensers 43 and 45 to the output of the primary. Due to the prevention of the re-ignition of .the spark gap by secondary reaction, the resultant wave form is substantially linear, The inductances 36 and 38 .in the primary circuit are inductively or electromagnetically coupled to the inductance in the secondary. The secondary, through the condensers 43 and 45, is electrostatically coupled to the primary, thereby producing a phase differ- .ence of between the primary and the secondary. The inter-action between the primary and the secondary, in the present arrangement in the circuit of the invention results in .a neutrodyne action.

While specific details of the system have been herein shown and described, the invention is not confined thereto as changes .and alterations may "be and may become apparent to those skilled in the art without departing from the spirit thereof as definedby the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States, is:

1. A radio transmitter of the class described employing a spark gap, a series resonant primary circuit connected to said spark gap, a parallel resonant secondary circuit, and electrostatic coup'l'ing means for coupling said primary to said secondary.

2. A radio transmitter of the class described employing .a primary circuit comprising a pair of .inductances and a condenser serially connected to a spark gap, a secondary circuit consisting of .an inductance connected in parallel with a condenser, and electrostatic means for coupling said secondary to said primary to obtain a transmitter output having a substantially linear wave shape in wavelengths shorter than about ten meters.

3. A radio transmitter of the class described employing a primary circuit comprising a pair of inductances and a condenser serially connected to a spark gap, a parallel resonant secondary circuit, and electrostatic means for coupling said secondary to said primary to obtain a transmitter output having a substantially linear wave shape.

4. A radio transmitter of the class described employing .-a series resonant primary circuit, a parallel resonant secondary circuit consisting of an inductance connected in parallel with a condenser, and electrostatic means for coupling said secondary to said primary to obtain a transmitter output having a substantially linear wave shape in wavelengths shorter than ten meters.

5. A spark gap type short wave generator comprising a series resonant circuit in the primary circuit, a parallel resonant circuit in the secondary circuit, and a capacitative coupling between said primary and the secondary circuits of the generator to restrict passage of energy from the secondary circuit to the primary circuit tending to effect re-ignition of a spark, said coupling producing a neutrodyning action.

6. A short wave generator of the class described employing a primary circuit having a spark gap connected across the output thereof, a secondary circuit having its input connected to the output of said primary circuit, certain of the elements in the primary circuit and the secondary circuit being electromagnetically coupled, and certain means for connecting the input of the secondary circuit to the primary circuit comprising electrostatic coupling means to produce a phase difference of 180 between said primary and said secondary to the end that said phase difference prevents secondary discharges across the spark gap, thereby resulting in a substantially linear output of the wave train.

7. A short wave generator of the class described employing a primary circuit having a spark gap connected across the output thereof, and a secondary circuit having its input connected to the output of said primary circuit, certain of the elements in the primary circuit and the secondary circuit being inductively coupled, and certain means for connecting the input of the secondary circuit to the primary circuit comprising capacitive coupling means to produce a phase difierence between said primary and said secondary to the end that said phase difference substantially restricts secondary discharges across the spark gap, thereby resulting in a substantially linear output of the wave train.

GEORGES AHIER. EMILE TOURATON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

